Radio controlled (RC) devices, including radio controlled model vehicles, such as cars, boats, helicopters and planes are enjoyed by hobbyists recreationally and competitively. Referring to FIG. 1, a radio controlled system 100 known to the art is shown. Conventional radio controlled system 100 may include a radio controlled device 110 and a hand-held controller 120. The radio controlled device 110, such as a car, is typically controlled by a user through the use of a hand-held controller 120 that transmits radio signals corresponding to the user's input to a radio receiver component of the radio controlled device. This allows the user to control a speed and direction of movement of the radio controlled device 110 via the hand-held controller 120.
A common problem associated with conventional RC devices is the disruption in the radio signal between a hand-held controller and the receiver of the radio controlled device. For instance, conventional radio controlled devices may have a limited range of operation. Additionally, radio signals may be disrupted due to interference caused by noisy motors, speed controllers, garage door openers, wireless communication devices and the like.
Another source of interference is produced by other radio signals for other radio controlled devices. It is commonplace for several users to be operating radio controlled devices in the same geographical area. FIG. 2 depicts multiple radio controlled systems 200 in the same geographical area. For example, races of radio controlled devices may be held on a track with several contestants. Conventional RC devices monitor an assigned frequency, such as 27.9 megaHertz (MHz), for a signal. Two devices operating next to each other on the same frequency may cause loss of control and may cause a collision of the devices. For example, hand-held controller 210 operating with radio controlled device 220 may cause interference between hand-held controller 230 and radio controlled device 240. Transmitters and receivers are generally equipped with frequency crystals, allowing a transmitter to send signals to a receiver on a specific frequency. The purpose of these crystals is to ensure that signals from one device do not interfere with signals from another device. However, crystals are costly for RC device operators, and frequency monitoring is an additional undesirable limitation. Additionally, frequencies must be assigned to operators before operation of an RC device, causing a delay before operation may begin. This may significantly reduce practice time for professional RC device operators and negatively impact the enjoyment of hobbyists.
With respect to radio controlled aircraft devices, another disadvantage of conventional transmission methods is multipath fading. Multipath fading may occur when a radio wave follows more than one path between a transmitter and receiver. Propagation paths may include a ground wave, ionospheric refraction, re-radiation by the ionospheric layer and other such paths. Because of the various obstacles and reflectors in a wireless propagation channel, a transmitted signal, or signals, may travel different paths and arrive at a destination point at different times and from different directions. Specifically, signals that are received in phase may reinforce one another. However, signals that are received out of phase may produce a weak or fading signal. Further, the receiver will be subject to varying levels of signal reception as it moves around, caused by constructive and destructive addition of the impinging waves due to their different phase offsets. Conventional RC aircraft device systems are subject to fading signal loss, potentially causing damage or destruction of the aircraft device.
Radio controlled aircraft devices may also be subject to intersymbol interference (ISI). ISI may be caused by multipath fading and is generally known as frequency fading due to time dispersion. Time dispersion sets a time limit on the speed at which modulated data bits or symbols may be transmitted in a channel. Because of the dispersion, symbols may collide and result in distorted output data. Differences in delay between various reflections arriving at the receiver may be a significant fraction of the data symbol interval, establishing conditions for overlapping symbols. ISI may occur if the data symbol duration is the same magnitude or smaller than the delay spread of the channel. As the data rate increases, the number of symbols affected by ISI increases. A receiver may not be capable of reliably distinguishing between individual elements and, at a certain threshold, ISI may compromise the integrity of received data. Because conventional RC aircraft devices cannot resolve multipath fading, they are unable to prevent intersymbol interference, resulting in transmitted data that may be substantially compromised upon arrival at a receiver.
Conventional radio controlled aircraft devices are also unable to prevent an aircraft device from operating according to an incorrect model program. A radio controlled device operator may be unable to determine the model program corresponding to his radio controlled device. While an aircraft device may function properly when operated under an incorrect model program under certain circumstances, an aircraft device operator may be more likely to lose control of the radio controlled device. A radio controlled aircraft device may be damaged or destroyed if an operator is unable to control the device, resulting in costly repairs or replacement of the device.
Consequently, a system and method for controlling RC devices which may provide a secure, interference-free link between receiver and transmitter, substantially eliminate fading, and provide model program detection and selection is necessary.